Deputies went to the backyard of a home in the 15800 block of Fairgrove Avenue after residents in the neighborhood just south of West Covina reported hearing loud noises about 10:20 a.m.
Authorities said at least 40 men ran in all directions.
About 50 roosters were found groomed for fighting, with about a dozen of them dead or dying. The remaining roosters had to be euthanized.
A small arena made of plywood and covered in plastic was also found.
Deputies also seized several razor-sharp metal talons, which often get tied to roosters' legs to make them more deadly.
"It's an unfortunate decision that people have made to take on gambling as opposed of the lives of the animals that were taken at this event," said sheriff's Lt. Raymond Enriquez. "It won't be tolerated by the sheriff's station or any law enforcement."
The three suspects, 67-year-old Frank Hernandez, 64-year-old Gamiz Concepcion and 63-year-old Eduardo Chaves, were arrested at the scene for being present during a cockfight. They were later cited and released.
Some neighbors said they never saw or heard any signs of the activity at the house.
"I'm absolutely shocked," Luis Medina said. "We've been living here 20, 30 years and not one cock-a-doodle-doo. So, yeah. A complete shock."
The sheriff's department is continuing to investigate to pinpoint the operators of the cockfight.